The field of the invention relates generally to regulating a microgrid, and more specifically, to methods and a system for regulating a microgrid in view of demand from an external grid.
A microgrid is a group of interconnected loads and distributed energy resources (DER) with clearly defined electrical boundaries that act as a single controllable entity with respect to the grid and can connect and disconnect to the grid to enable the microgrid to operate in both grid-connected and island modes. As microgrid installations steadily grow in specific pockets in the United States and around the world, widespread adoption of commercial microgrids would primarily rely upon the economic benefit to the owners and operators. New market rules (e.g., New York and California) have been introduced that facilitate the aggregation of sub-metered assets and accelerated integration of DERs into the grid. Accordingly, there is an increasing need and incentive for facilitating distributed assets to participate in grid ancillary service functions, such as, frequency regulation.
Power system frequency is a major indicator of power balance in the power system. A decrease in power generation in relation to the demand or load may cause the frequency to drop below a nominal frequency. Similarly, a decrease in demand may cause the frequency to increase beyond the nominal frequency. Furthermore, high penetration of intermittent energy sources, such as wind turbines and solar arrays, increases the potential for variability in system frequency. If the frequency deviates too far from the nominal frequency, equipment like pumps and motors run faster at the higher frequencies or slower at the lower frequencies. Some equipment will automatically shut down to avoid operational difficulties and accelerated maintenance. For example, in the event of a sharp decline in relation to power fluctuations, under-frequency load shedding controllers may operate to disconnect some or all of the associated loads.
To facilitate a functional and reliable grid, the Independent System Operators (ISOs) that operate the various regional grids must maintain their electric frequency very close to 60 hertz (Hz), or cycles per second (50 Hz in certain countries). Grid operators, therefore, seek to continuously balance power generation with demand to maintain the proper frequency. The imbalance between power generation and demand can be mitigated by use of microgrid resources. However, there are many constraints in utilizing microgrid resources that must be considered, such as cost to operate equipment, time to ramp up or ramp down power generation, and availability of resources.